1. Field of the Invention
This invention generally relates to integrated circuit (IC) and display backplane fabrication and, more particularly, to metal oxide semiconductor (MOS) thin film transistors made from doped of ZnOx, InOx, GaOx, and SnOx materials.
2. Description of the Related Art
Currently, a variety of materials are being used for oxide semiconductor based thin film transistors with metal oxide semiconductors (MOS) as the active semiconducting materials (see for example, “Transparent Electronics”, J. Wager, D. Keszler, R. Presley, Springer, 2007). At this time, the primary materials of choice include ZnO and InGaZnOx. Very good electrical performance can be obtained for thin film transistors (TFT) devices fabricated with these materials. For example, InGaZnOx TFTs can be used to drive pixels for electrophoretic, liquid crystal display (LCD), and organic light emitting diode (OLED) displays.
It should also be noted that these MOS materials are very closely related to transparent conducting oxides (TCO) materials, although the MOS materials are semiconducting due to their low carrier concentrations. A key aspect of this technology is to precisely control carrier concentrations in these MOS materials so that they are not too conducting, so that they can be switched off.
In the case of ZnO, very tight control over deposition conditions is necessary to obtain the appropriate semiconducting film characteristics. Unfortunately, InGaZnOx films are expensive to fabricate due to the high cost of the In and Ga used in the films.
It would be advantageous if inexpensive MOS materials were available for the fabrication of TFTs.